Tonight, a stunning look at children and fear in America. Every parent knows that watching a change suffer from fear and ç anxiety is bheart-wrenching. Ñ just getting out of the house can be an enormous struggle. Just this week, new ñscience, what you're about to see a very personal, powerful, and what we found at the end of thefá tunnel left us speechless. Reporter: Inside this suburban office building in new Jersey, a small yellow room, where a battle is about to play out right in front of our cameras. No! Reporter: 15-year-old Bridget looks like your typical teenager on the outside, but inside, she is wrestling to break free from unimaginable fear. And on this day, her progress is measured in inches. What do you think? It's like nine. Okay. Well, come on. Look at that. Reporter: Her therapist is measuring the couch for Bridget. You all right? Reporter: Every inch counts. You could lean against the -- Arm. Arm rest with your arm. From her elbow to her hand. It's good for you. Okay. Why don't you -- Reporter: The woman at the other end of the sofa is about to move from her chair to the couch. Tell me what's going on inside. She got so close. And she's never been this close before. She's never been this close before. She's sitting on the same -- Reporter: That woman who has Bridget so terrified is her own mother. Bridget believes her mother is somehow contaminated, and 1e Bridget's fear is that her mother will contaminate her too. Now, I want you to remember -- Reporter: Bridget has been diagnosed with obsessive compulsive disorder. Her particular obsession, an irrational fear that her own family is somehow contaminated. And because of the contamination, she can't be near them. I just have to prove to her that I can do this. Reporter: Who is Bridget talking about? The OCD, as if it were a person trying to control her. She's not gonna win this time because she's won too many times. She's just, it's just a trick and then this idea will go down. Reporter: But on this day, the OCD is still winning.g# She's just really close. Reporter: For Bridget, it's become all-consuming.o@ r(t&háhp &hc my life in the past six months. I haven't been able to be at home, touch any of my belongings that are at home. I haven't really seen any of my friends. Reporter: Long before the worries, Bridget was a beautiful little girl, smiling from ear to ear, growing up playing with her two older brothers, a star student at school in the gifted program, with a proud mother and father at home. A standout swimmer in the pool, a fish in the water. The first signs that all of this) Was beginning to crack came at a just 11, with what Bridget's mother, Karen, says was a need to be perfect at school. Everything had to be 100, or she had to know every spelling word. Then all of a sudden, she started to notice that her books had to be in a certain place, and she didn't want certain things touched. Reporter: She noticed that you were a bit of a perfectionist, had to do everything perfectly with schoolwork and -- surprisingly, we're able to stand right next to Bridget as we talked to her. Why us and not her own family? Her doctor says this proves just how irrational the OCD can be. Bridget's mind is fixated on her own family, and the OCD won't let go. Eighth grade, miraculously, it was pretty much better. So I stopped taking my medicine, I stopped going to the therapist. And then that's when this came up. Reporter: Her OCD would come back with a vengeance.÷ú and this time, her fear had morphed into contamination. The contaminati, and think about it as being something that's dirty, radiation or something like that. It spreads. Reporter: Bridget's doctor, Allen weg. In Bridget's case, how do you go from being a perfectionist to someone who can't touch her parents? Can't even be in the same home with them? It seems so extreme. You have to think about OCD ÷ú as sort of entering, entering a person's mind and looking around and saying, where can I cause trouble? And so, what better way for OCD to torture her than to say you can't be in the same home with your family. Reporter: The doctor reminds Bridget to keep her eye on the prize and all of the things she's had to give up, her family. It's been four months since she's been home. She lives with her grandmother nearly an hour away. And all of that swimming she loved, that time in the pool, she's been forced to give that up too. She can go an inch. Reporter: All right. Let's just do an inch. Inch? Yeah. This way? Yes. All right.p that's about an inch right from her. Reporter: For so many parents, it is excruciating -- watching their children suffer, not knowing if they'll ever break away from their fear. It's overwhelming. That's really what it is, how it encompasses everything in your life and how I didn't realize it could grow to where it's, where it is now. Reporter: The treatment we're allowed to witness is rarely shown on camera. It's what's called exposure and response prevention therapy. Bridget must expose herself to iñ her fears to desensitize herself, getting closer to her mother one inch at a time.6z I feel helpless for her. I want to reach out and touch her and hold her. And that's the one thing that I can't do to try to make her feel better. Breathe through this. It's the last one for the day. Reporter: Bridget can't even speak. She whines and shakes on the couch. She doesn't want her mother to talk either. No, don't. Don't. Okay. Now, your mom is sitting on the couch with you in my office. Reporter: For Bridget, this in and of itself is remarkable progress. During her last visit, her mother couldn't even sit on the couch at all. It's a trick of the brain pretty much.t( like, my mom just sitting on the couch is no big deal.ñ the OCD makes you believe more fear than there actually is. Reporter: And Bridget is hardly alone in her fight against fear, her fight against ocd.my Rocco decorso was just eight years old when his mother took this video of him. Mom, what did you say before? I don't remember. Get the phone. Mom! I don't remember. Please get the phone. Reporter: Rocco's obsession revolves around the fear of getting sick, the fear about what could happen when he leaves for school. Say, what did you say? I don't remember. Mom. I don't know what I said, honey. Mom. I don't remember exactly what I said. Mom, what did you say? Reporter: The fear is relentless. He wants her to promise him nothing bad is going to happen. I can't answer you anymore.ym Are you sure nothing bad is gonna happen? Rocco, what did I say? Reporter: He begs his mother to repeat herself. Even for the most loving of moms, it can break you. I don't remember what I said. I don't know what I said. Mom. Why do you do that? Reporter: His mother taking this video to show the doctor what they go through every morning together. These images captured just weeks before:%s diagnosis. Rocco has OCD, too. His fear of what if consumes him. And what about my day? Rocco, I don't -- Reporter: His parents told us it started when he was just five. I'll never forget going to a carnival, he was on a merry-go-round crying.ym like, you're supposed to have fun. Why is this kid crying? Even now, at times when he ç asks the questions, it's really hard to have the patience. I mean, you know, we try. And sometimes you run out of patience. Sometimes, you know, like get over it, knock it off, already, you know? Sometimes you lose your patience. Honey, I don't know what you're saying. I don't remember what I said about the day. You'll have a great day. Why do you do this?koñ I said a -- I said a couple of things. The difficult part is he's five years old. He says, "I can't live like this no more." Coming from a 6-year-old saying, "I can't live like this. I want to live with god.fá don't worry, mommy and daddy, I'll look down after you." That's tough. Reporter: His parents tormented, watching their little boy struggle to get past his anxiety. All of this worry, and on this lúf=i9%91 for the school bus yet. Go. Good-bye. Reporter: We met Liz ç mcingvale, too. For her, m)uáu O get out of bed for school. Just 15 when she was diagnosed, her obsession is being clean.I] Scrubbing herself until her skin is raw, and just one round of it is never enough.]I I have to do it again, all over, because I feel like my hair touched the side of my arm, which my arms are all contaminated. So -- and this is just the beginning. Reporter: So frustrated, some mornings, she punches holes in the wall. Even with all this washing, Liz 8 still has to take a shower and pick out her outfit.÷ú Some of these various shirts on this side are contaminated. This grey one is -- Reporter: It takes several hours, even on a good day, just to get out of the house. Actually, I have to wash my hands again because I accidentally touched that shirt. So -- My name is Michelle. I'm 14 years old, and I have OCD. Reporter: And finally, we met Michelle, who is unable to go to school. It's hard for her to leave the a!=um9ñ Would we be able to open the door or roll down the window?

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